The present invention concerns a locking mechanism for securely engaging two components of a bone prosthesis, such as a plastic socket insert within a metal support shell of an acetabular cup prosthesis.
Present day acetabular prostheses often comprise the combination of a plastic cup adapted for receiving a femoral head nestled within a metallic support shell adapted for implantation in the acetabulum. Various means have been provided for receiving the cup within the shell. For example, in U.S. Pat. No. 4,172,296, detent means on the inner surface of the shell engage an annular groove on the outer surface of the cup to permanently affix the cup within the shell; with such means, however, disassembly of the two components is impossible without destruction of the insert. In U.S. Pat. Nos. 3,863,273, 4,051,559 and 4,408,360, an annular protusion or tab on the outer surface of the insert snaps into an annular groove in the inside surface of the shell to hold the cup within the shell. Such designs, however, allow some axial and rotational movement of the cup within the shell. A need therefore still exists, and it is the primary object of the present invention to provide, for a mechanism for joining such components which eliminates their relative axial and rotational movement in the assembled prosthesis but permits its disassembly without damage to the components.
U.S. Pat. No. 4,231,120 discloses a nonrigid orthopedic component secured in cancellous bone by flexible ribs on the component producing an interference fit upon insertion of the component into a substantially complementary but slightly undersized recess in the bone.